Diazo printers have been known for many years, and are especially effective for producing high-accuracy whiteprints from original materials to be printed. In such printers, a sheet of printing paper and an overlying sheet of original material to be printed are conveyed by a motor-driven roller system through a position in which they are exposed to ultra-violet radiation from a suitable ultra-violet lamp, after which the original document and the copy paper are separated from each other; the original is returned to the machine user, while the copy paper is moved, again by the motor-driven roller system, through a developer chamber in which it is exposed to a mixture of ammonia and water vapor. Upon exit from the developing chamber, the copy paper carries an accurate reproduction of the information contained upon the original copy.
In order to obtain proper image reproduction, it is important that the ammonia be delivered to the developer chamber at a sufficiently high rate. The minimum rate of delivery of ammonia to the developer chamber which produces satisfactory results increases with the speed at which the copy paper is moved through the developer chamber. It is possible to set the rate of ammonia delivery at a fixed value which is adequate for any contemplated speed of the copy paper, but if this fixed rate of delivery is set high enough for the higher range of speeds of the copy paper then it is excessive for speeds of the copy paper in a lower range. Not only would such an adjustment waste ammonia, but some of the excess ammonia may be discharged to the room, where it would be highly objectionable, or special expensive provision would have to be made for its removal.
It has therefore been common in the past to set the ammonia delivery rate at a first relatively lower value when the copy paper speed is in a lower range of speeds, e.g. 0-40 feet per minute, and to adjust it manually to higher levels if higher copy speeds are utilized, e.g. 40-60 ft./min. This not only requires an operator to make such adjustments in ammonia delivery rate, but as a practical matter often results in pollution of the room with excess ammonia vapor when the speed of the copy paper is decreased and the operator forgets or otherwise fails to turn down the ammonia delivery rate.
Accordingly, it is an object of the invention to provide a new and useful ammonia supply system which assures that the ammonia delivery rate will be increased appropriately when the copy paper speed increases into a higher range of speed, and which assures that the ammonia delivery rate will be cut back or reduced when the speed of the copy paper through the developer chamber is reduced into a lower range.
A further object is to provide such a system which does not require careful monitoring by an operator, and in fact does not require an operator to adjust the ammonia delivery rate at all.